The invention relates to a pressure-control valve according to the preamble of claim 1.
A pressure-control valve of this kind is known from DE 195 12 143 C1. In this valve the hydraulic fluid pressure which is to be regulated acts on a check piston in a working chamber. This check piston is pushed into a seat by a preloading spring. If the pressure exceeds a certain value, the check piston is raised from its seat and clears a hydraulic fluid discharge point to a discharge opening. The pressure is limited to a certain value through the discharge of a volumetric flow which does not have to overcome any dynamic resistance. However this method, which is most simple in terms of basic system, of regulating a pressure, i.e. allowing a quantity of hydraulic fluid which causes the excess pressure in a system to run off in a volumetric flow, since it cannot be taken up by appropriate consumers, has the disadvantage of resulting in a loss of capacity and possibly heat production in the overall system. It is therefore more favourable and desirable to limit a volumetric flow by regulating the volumetric delivery of hydraulic fluid instead of limiting the pressure in the hydraulic systems by letting this flow run off.
A construction of a pressure-relief valve which comprises a second pressure chamber and a second valve is known from DE-OS 20 42 094. This second valve, which is called a pilot valve, regulates the opening and closing of a first valve, which clears a cross section to discharge a volumetric flow of the hydraulic fluid. The first valve consists of a sleeve as valve piston, which is pushed against a seat by a first preloading spring. A throttle bore is located centrally in this valve sleeve, via which bore the pressure chamber whose pressure is to be measured and regulated is connected to a second pressure chamber. The second pressure chamber is connected to the second valve, which comprises a cone which is pressed against a seat by a second preloading spring. The pressure in the first and the second pressure chamber is equal as long as the second valve is closed. The valve sleeve of the first valve is pressed against its seat by the preloading spring. If the pressure which acts on the second valve in the second pressure chamber via the throttle now exceeds a preset value, the second valve will open. The hydraulic fluid can now run off and the pressure in the second pressure chamber drops significantly, as only a small quantity of hydraulic fluid can continue flowing via the throttle bore. Pressure therefore only acts on the valve piston of the first valve, the sleeve, from one side, namely the first pressure chamber. It lifts off its seat and clears the valve flow opening. The advantage of a valve construction of this kind with a pilot valve lies in the fact that the valve responds well. However the prior art described in this publication entails the disadvantage of also letting a volumetric flow run off to regulate the pressure. Moreover, the pressure at which the valve opens can only be regulated via a screw against which the second valve spring is supported. Neither adjustment during operation nor remote adjustment is possible.
The object of the invention is therefore to provide a pressure-control valve according to the preamble of claim 1 whose regulation pressure can be continuously and remotely adjusted and which regulates an actuating variable, so that the pressure in the system can be regulated by this actuating variable, for example the actuating pressure of a hydraulic pump.
This object is achieved according to claim 1 by a pressure-control valve with a first control piston, which is disposed between a first pressure chamber, which adjoins the first control piston and is connected to at least one working line, and a second pressure chamber, which adjoins the first control piston. This first control piston is pushed against a first seat by a first preloading spring, a throttle connecting the first and the second pressure chamber. The second pressure chamber is connected to a second control piston, which is preloaded by a second preloading spring and which, when a predetermined pressure in the second pressure chamber is exceeded, is displaced to an extent such that a control edge of the second control piston clears a discharge point of the second pressure chamber. Here the first control piston comprises a control edge which connects an actuating pressure line to a hydraulic fluid discharge point when the control piston is displaced against the first preloading spring. An actuator, which is regulated by a control signal, presses onto the second control piston against the second preloading spring.
A pressure-control valve according to the invention can be remotely regulated in a favourable manner, as the actuator can be regulated via a control signal and the regulation pressure determined via this actuator. Advantageous developments and configurations of the invention are indicated in the subclaims.
The pressure-control valve advantageously only regulates one actuating pressure line, via which the capacity of a feed pump which builds up and maintains the hydraulic pressure is regulated downwards. Thus the pressure is regulated in the system not just through the discharge of a volumetric flow which simply flows back from the feed pump into the hydraulic system via the pressure-regulating valve to a storage tank or the pump intake side while giving rise to a loss of capacity and therefore emitting heat.